1. Field of the Invention
The present invention relates to a fuel cell usable as a power source for an electronic device or the like.
2. Description of the Related Art
Currently, secondary batteries, such as lithium ion batteries, are mainly used as power sources for electronic devices, such as portable notebook personal computers, mobile devices, etc. These modern electronic devices have increasingly higher functions and require increased power consumption and longer operating time. To meet these requirements, compact, high-output fuel cells that require no charging are expected as novel power sources. There are fuel cells in various forms. A direct methanol fuel cell (hereinafter referred to as DMFC) that uses a methanol solution as its fuel, in particular, has an advantage over one that uses hydrogen as its fuel in enjoying easier fuel handling and simpler construction. Thus, the DMFC is a currently noticeable power source for an electronic device.
Normally, a DMFC has a housing that houses a generator section for actual power generation and a control circuit section that controls the operation of the generator section. The generator section is provided with a fuel tank, mixing tank, liquid pump, air pump, etc. The fuel tank contains high-concentration methanol. The methanol in the fuel tank is diluted with water in the mixing tank. The liquid pump pressure-feeds the methanol that is diluted in the mixing tank to an electromotive unit. The air pump is used to supply air to the electromotive unit. The electromotive unit has an anode and a cathode. It generates power based on a chemical reaction by feeding the diluted methanol and air to the anode and cathode sides, respectively. As this is done, the electromotive unit is heated to a high temperature by the reaction heat that is produced by a chemical change.
The control circuit section is provided with a printed circuit board in the housing and semiconductor devices mounted on the circuit board. According to a fuel cell described in Jpn. Pat. Appln. KOKAI Publication No. 7-6777, for example, heat that is produced by power generation is discharged into the housing via the surface of the electromotive unit and anode and cathode passages. Air in the housing is discharged for ventilation with a cooling fan or air blower that is attached to the inner surface of the housing.
When the fuel cell constructed in this manner is connected to an electronic device to be operated, a battery of the device is used as an auxiliary power source, since the fuel cell has no auxiliary battery therein. When the electromotive unit of the fuel cell is not in power generating operation, the fuel cell cannot singly provide any auxiliary power source for driving the air pump, liquid pump, solenoid valves, etc.
If the fuel cell is separated from the electronic device while it is operating with the electromotive unit not in power generating operation, therefore, all the pumps, valves, etc. stop in their active state. All of valves for preventing backflow and leakage in liquid and air passages are open during the operation of the fuel cell. If the run is stopped in this state, all the valves are inevitably kept open. If the fuel cell is transported or turned upside down in this state, liquids such as fuel in the fuel cell may possibly leak out. In some cases, moreover, the liquids may flow back in the fuel cell, thereby causing problems in the pumps or other equipment.